In a working machine, foreign matters such as metal powder (being so-called “chips”) are generated during processing of a workpiece. These foreign matters are usually returned together with a coolant to a coolant tank. Here, although a large foreign matter is captured/discarded by a strainer or the like, a relatively small foreign matter (chips or the like) can penetrate or pass through a strainer or like and floats in a coolant as a so-called “contaminant”. Further, various kinds of airborne dust in air may be mixed into this coolant in some cases.
In a machining center of a numerically controlled lathe, a coolant is injected from a tool end, a workpiece or a tool is cooled, discharge of chips is enhanced, and a machining speed or a machining accuracy is improved. In this case, in order to protect a coolant circulation pump or maintain a machining accuracy, a cyclone filter or a filter element type filter is used.
In a case that a filter element type filter is used, a contaminant such as a fine scrap metal mixed in the coolant clogs the filter. Therefore, periodical maintenance, such as replacement of the filter or cleaning of the filter, is required.
Although use of a cyclone filter can be considered in order to eliminate the need for the maintenance, e.g., the replacement of the filter or the cleaning of the filter, filtration of the cyclone filter is not satisfactory, and there are disadvantages of a cyclone filter, for example, operation thereof is limited in oil, and light dust like airborne dust in air can not be filtered.
Therefore, in a working machine, in a case that highly precise filtration is required, use of a filter provided with a filter element is unavoidable. However, as described above, there are problems that a cycle for the replacement or the cleaning of the filter is short and that a running cost is thereby expensive. Therefore, a filter which does not have to be frequently cleaned has been desired.
However, an effective filter that does not have to be frequently cleaned, that removes foreign matters adhering to the filter efficiently, that eliminates clogging, or that prevent such clogging, has not been suggested yet.
As a prior art for cleaning a filter, for example, there is a prior art in which a filter rotates and removes foreign matters adhering thereto by using centrifugal force (Refer to Patent Literature 1).
However, according to this prior art (Patent Literature 1), since power used for rotating the filter is additionally required or a rotation transmission mechanism for transmitting rotation from a rotary drive source for a pump to filter is additionally required, an amount of energy consumption increases and constructions thereof are complicated.
Furthermore, although a foreign matter having large specific gravity like a metal can be removed from a filter surface by the centrifugal force, a foreign matter having small specific gravity like so-called “dust” or “dirt” cannot be removed from the filter surface by centrifugal separation, because the centrifugal force acting thereto is small.
Moreover, there is a situation where fine foreign particles that have once passed through the filter are pressed against a filter inner wall by the centrifugal force, and therefore, it is possible to generate clogging in the filter.